Crater Lake National Park is near the midpoint of the Sierra-Cascade Mountain Province of the Pacific Mountain System. The climate of this province is characterized by cool summers and
moist winters with heavy snowfall. The park lies astride the backbone of the Cascade Mountains near the southern extremity of their higher elevations with the general topography dropping 1,000 to
1,500 feet a short distance to the south. The crest of the mountains acts as a barrier to the prevailing frontal systems which approach the area from the North Pacific Coast.

The park is slightly south of the main storm track for these fronts, but still well within their belt of influence. These storms, together with the normal eastward movement of air
across the region, are constantly bringing in a fresh supply of nearly saturated air whose temperatures closely approach those of the Pacific Ocean over which it has been traveling.

explanation of general weather pattern for year

From late fall until early spring, the land masses become much colder than the ocean. Incoming air masses cool rapidly as they move up the slopes of the Cascade Mountains because of
the colder ground and the increasing elevations. As the air cools, great amounts of precipitation are released. From late spring through early fall this situation is reversed, with the land being
warmer than the overlying and incoming air mass. Due to ground heating, and despite the cooling caused by increased elevations, the temperatures at the crest of the range are considerably higher than
the air crossing the coastline. As a direct result, the air becomes drier as it moves inland and up the west flank of the Cascades. This dry air situation is further exacerbated by a nearly total
absence of large-scale moisture-laden storms during this time of year.

Rainfall, snowfall, and temperatures within the region of the park vary significantly with differences in elevation and are strongly modified by the rain
shadow configuration of the Cascade crest and the distance of the recording area from it. Table 3 shows comparative climatic data for the Crater Lake region. There is a steady decline in the mean
annual temperature for all recording stations at higher elevations. Precipitation increases with increasing elevation but the total amounts are strongly influenced by the station's relationship to the
morphology of the Cascade crest.

There is a greater range in mean annual totals of precipitation in the area of the park than there is in the entire northeastern quarter of the United States. The most rapid change in
precipitation amounts within the park takes place down the eastern flank, where the heavy precipitation of the High Cascades gives way to the semiarid high plateau country of central Oregon.
Topographic lows in the Cascade crest allow greater amounts of precipitation to fall at Fort Klamath on the south flank of the park, but Chemult, Chiloquin, and Klamath Falls to the east remain
relatively dry.

summer

Warm, clear days characterize the summer months in the area of Crater Lake National Park. At the rim of the caldera the daytime summer temperatures are very moderate. They average 60°
to 701F and seldom exceed 85

0F. Since 1926, the record high temperature at park headquarters in Munson Valley has only been 911F. Evenings
are crisp, with the temperature dropping into the 40's and 50's on most nights, and taking an occasional plunge to- freezing during any of the summer months. Daytime temperatures in the Panhandle area
during the summer are often 10 or more degrees warmer than those at the caldera rim because of the elevation difference.

Only about 6 percent of the annual precipitation falls from June through August, and on the average, only about five days during this period will have precipitation greater than 0.10
inch. Summer thunderstorms seldom strike with enough force or volume to produce damaging rains or accompanying hail. Traces of snow have fallen in the park during all of the summer months.

Soils throughout the park are at their field capacity for water retention shortly after the melting of the heavy winter snows. Because of the dry summers, the soil moisture
progressively declines so that maximum moisture stress on vegetation depends upon the length of rainless periods and upon the evapotranspiration rate during the warmer season.

winter

As is true for most of Oregon, the park has a very definite heavy bias toward winter precipitation. Approximately 70 percent of the annual precipitation falls from November through
March in the park, and practically all of it falls as snow. Snow depths of 100 to 200 inches on the ground are common at park headquarters, and the annual total snowfall is nearly 600 inches. In about
half of the winters, the first measurable snowfall in Munson Valley can be expected by the end of September, and at the park's lower elevations by the end of
October. The greatest snow depth ever recorded in Oregon was 242 inches and that was in the rim area of Crater Lake at an elevation of 7,086 feet. Snow loads may reach 500 pounds per square foot on
structures in Munson Valley and be only slightly less in the vicinity of Annie Springs. Measurable snowfall can be expected in Munson Valley on about 100 days each year, and up to 37 inches of snow
have fallen in one 24-hour period (Sternes, 1963).

Daytime temperatures during the winter months average only slightly above freezing in Munson Valley and throughout much of the park, with nighttime temperatures dropping to between 170and 201F. Maximum temperatures of 50° to 600 and minimums of 0° or lower may both be expected occasionally during the winter months. The lowest minimum
temperature recorded in the headquarters area of Munson Valley since 1926 has been 210F.

On the lower eastern slopes of the park, the annual snowfall drops to 25 to 65 inches. These lower eastern elevations also receive the lowest winter temperatures due to the stagnant
pooling of cold air, the invasion of Arctic fronts from the northeast, and the comparatively warm marine air of higher elevations gliding over the colder air mass instead of pushing it away.